Hendra Virus (HeV) is a recently identified paramyxovirus that has been identified as a P4 pathogen and added to the DHHS Select Agents list and the NIAID Priority Pathogens list. Like other paramyxovirus fusion proteins, the Hendra Virus F protein (HeV F) has been demonstrated to promote viral membrane fusion. HeV F is synthesized as a precursor protein, F0, which is cleaved into the F1 and F2 subunits (Michalski et al., 2000). This processing has been demonstrated to be essential for fusogenic activity in other viral systems. The HeV F protein appears to undergo incomplete processing, with a substantial amount being incorporated into virions in the uncleaved state. The goals of these investigations are to characterize the proteolytic processing of HeV F protein and to determine how the cleavage state of the protein affects fusogenic activity. Specific aim 1 will examine the expression and cleavage state of HeV F on the cellular surface and analyze the nature of this uncleaved protein. Experiments in aim 2 will determine the amino acid residues that are key to proper proteolytic processing. Finally, the effect that uncleaved HeV F protein on the surface has on the fusogenic activity will be analyzed in aim 3. [unreadable] [unreadable]